This application is based on Japanese Patent Application No. 11-98046 filed Apr. 5, 1999, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to a method and an apparatus for fixedly connecting together an externally threaded tube and an internally threaded tube by tight engagement of an externally threaded portion and an internally threaded portion provided on the externally and internally threaded tubes, respectively. The present invention is applicable to operations to connect any threaded tubes, but is preferably applicable to operations to connect tubes having comparatively large lengths and diameters, for obtaining pipes used to support earth drilling tools for drilling or boring the earth in oil fields, and fluid transporting pipes used for transporting oils, natural gases and other fluids.
2. Discussion of the Related Art
As a method of fixedly connecting together two tubes, there is known a method wherein an externally threaded portion of an externally threaded tube and an internally threaded portion of an internally threaded tube are first brought into engagement with each other and are then rotated relative to each other so that the two tubes are fastened or fixedly connected to each other. Three typical examples of this method are as follows:
1) The threaded surfaces (hereinafter referred to as xe2x80x9ccontacting thread surfacesxe2x80x9d of the externally and internally threaded portions of the two tubes are held in meshing engagement with each other, with an axial tightening force acting between the contacting threaded surfaces, while shoulder surfaces of the two tubes are held in contact with each other at their contacting portions (hereinafter referred to xe2x80x9ccontacting shoulder surfacesxe2x80x9d);
2) The contacting thread surfaces of the two tubes are held in meshing engagement with each other, with an axial tightening force acting between the contacting thread surfaces, and a non-threaded tapered outer circumferential surface (a radial sealing surface) of the externally threaded tube and a non-threaded tapered inner circumferential surface (radial sealing surface) of the internally threaded tube are held in engagement with each other, with a radial tightening force acting between the tapered outer and inner circumferential surfaces, while the contacting shoulder surfaces are held in contact with each other; and
3) The externally and internally threaded surfaces of the two tubes which are both tapered are held in meshing engagement with each other, with a radial tightening force acting between the contacting thread surfaces of the two tubes, without the contacting shoulder surfaces being provided on the two tubes.
Where the two tubes are fixedly connected together by the method 1) indicated above, a fluid-tight sealing is provided between the contacting shoulder surfaces of the two tubes. Where the two tubes are fixedly connected together by the method 2) indicated above, a fluid-tight sealing is provided both between the contacting shoulder surfaces, and between the radial sealing surfaces. In view of these facts, a tube assembly obtained by connecting the two tubes by the method 1) is suitably usable as a drill pipe for supporting earth drilling or boring tools, and a tube assembly obtained by connecting the two tubes by the method 2) is suitably usable as a fluid transporting pipe. The tube assembly obtained according to the method 2) wherein the sealing is provided between the radial sealing surfaces exhibits higher degrees of fluid tightness and fluid leakage resistance, than the tube assembly obtained according to the method 1) wherein the sealing is provided between the contacting shoulder surfaces.
Where the method 2) is applied to two tubes each of which has two shoulder surfaces that are spaced apart from each other in the axial direction, the axially corresponding shoulder surfaces of the two tubes are usually held in contact with each other. Of the four shoulder surfaces of the two tubes, one of the two shoulder surfaces of the internally threaded tube which is located at the outer or distal end of the internally threaded portion, and one of the two shoulder surfaces of the externally threaded tube which is located at the inner or proximal end of the externally threaded portion are referred to as xe2x80x9ctorque shoulder surfacesxe2x80x9d. Each of the two tubes has a radial sealing surface in the form of a non-threaded tapered inner or outer circumferential surface between the two shoulder surfaces. When the two tubes each having the two shoulder surfaces and the radial sealing surface are connected together according to the method 2), the axial tightening force acts on the tubes at two axial positions corresponding to the two sets of contacting shoulder surfaces, and the radial tightening force acts on the tubes between the contacting radial sealing surfaces. Since the fluid-tight sealing is provided primarily by the contacting radial sealing surfaces, the method is called a radial sealing method [Method 2)-1]. Depending upon the dimensional relationships of the radial sealing surfaces and the shoulder surfaces of the two tubes, it is possible that only the torque shoulder surfaces of the two tubes are held in contact with each other, with the other shoulder surfaces being held in an axially spaced-apart relationship with each other.
Where the two tubes are not provided with the torque shoulder surfaces, it is possible that the axial tightening force acts between the contacting shoulder surfaces, while the radial tightening force acts between the radial sealing surfaces. In this case, the fluid-tight sealing is provided primarily by the contacting shoulder surfaces, and therefore the method is called a shoulder sealing method. Tube assemblies obtained according to this shoulder sealing method and the above-indicated radial sealing method are referred to as premium joints, and these methods are called a premium joint method [Method 2)-2].
The specific method that can be suitably used for fixedly connecting together the two tubes depends upon the configurations of the threaded portions of the two tubes and the configurational and dimensional relationships of the threaded portions and the shoulder surfaces. Not only the method 3) but also the methods 1) and 2) may be used where the threaded portions of the tubes are tapered. Usually, the method 1) is used for the tubes whose threaded portions have trapezoidal or triangular threads, and the methods 2) and 3) are used for the tubes whose threaded portions have trapezoidal threads. The externally and internally threaded tubes may be called a xe2x80x9cpinxe2x80x9d and a xe2x80x9cboxxe2x80x9d, respectively.
Although an operation to fixedly connect together two threaded tubes is desirably controlled on the basis of the axial and radial tightening forces, this control is difficult. Conventionally, therefore, the tube connecting operation is controlled on the basis of a wrenching torque applied to rotate the two tubes relative to each other, or both the torque and a speed of the relative rotation.
Where the tube connecting operation is controlled on the basis of the wrenching torque, the relative rotation (wrenching operation) is terminated when the actual wrenching torque (torque equal to a resistance to the relative rotation) has become equal to a desired or target value. In this case, the desired wrenching torque value corresponding to a desired tightening force of the two tubes is calculated on the basis of a measured or estimated coefficient of friction at the contacting portions (contacting thread surfaces and contacting shoulder surfaces) of the two tubes. However, the friction coefficient greatly varies depending upon the physical conditions (e.g., roughness) of the contacting surfaces as machined, the lubricating conditions of those contacting is surfaces, and other conditions, which vary under different machining conditions and under different environments in which the tube connecting operation is carried out. Accordingly, the actual tightening force tends to have a considerable variation from the desired or nominal value for the tube assembly to be obtained. Thus, it is difficult to obtain the tube assembly having the nominal or desired tightening force, and the conventionally obtained tube assembly suffers from problems of yield and seizure at the contacting surfaces.
In one example of control of the tube connecting operation on the basis of both the wrenching torque and the relative rotation speed, an upper limit and a lower limit are set for each of the wrenching torque and the relative rotation speed, for defining their optimum ranges. The tube connecting operation is determined to be performed in a normal manner, if the relative rotation speed is in the optimum range when the wrenching torque has reached its lower limit, or if the wrenching torque is in the optimum range when the relative rotation speed has been lowered to its lower limit. If either of the above two conditions is not satisfied, the tube connecting operation is determined to have some abnormality. The relative rotation speed used to effect the above determination is a value detected after the externally and internally threaded tubes have been brought to a predetermined state, which may be: a predetermined state of initiation of the meshing engagement of the externally and internally threaded portions; a state of the meshing engagement established after the two tubes has been rotated relative to each other through a predetermined angle after the initiation of the meshing engagement; or a state in which the wrenching torque has reached a predetermined speed detection initiating value at which the detection or measurement of the relative rotation speed is initiated. The speed detection initiating value may be the wrenching torque value detected when the shoulder surfaces or radial sealing surfaces of the externally and internally threaded tubes have been brought into contact with each other after the thread surfaces are in substantial meshing engagement with each other. The control of the tube connecting operation on the basis of both the wrenching torque and the relative rotation speed makes it possible to detect abnormalities of the tube connecting operation, such as an abnormal increase of the wrenching torque (up to its upper limit) before full engagement of the externally and internally threaded portions, which may occur due to foreign matters interposed between the external and internal thread surfaces, and an abnormally high value (upper limit value) of the relative rotation speed when the wrenching torque is not larger than the lower limit.
However, the conventional method and apparatus for fixedly connecting together the externally and internally threaded tubes suffer from a considerable large amount of variation of the final wrenching torque due to a variation of the friction coefficient of the individual tubes, since the measured or estimated friction coefficient is used to determine the speed detection initiating value of the wrenching torque, and the lower and upper limits of the wrenching torque. Accordingly, the conventional method and apparatus do not permit accurate detection of abnormalities in the tube connecting or wrenching operation.
It is therefore an object of this invention to improve the reliability of control of the operation to fixedly connecting together the externally and internally threaded tubes. The present invention provides the following forms of a method of fixedly connecting the externally and internally threaded tubes, the following forms of an apparatus for practicing this method, and the following forms of a recording medium storing a program for controlling the operation to fixedly connecting the tubes. Like the appended claims, each of these forms of the present invention is numbered and depends from the other form or forms, where appropriate, to indicate possible combinations of technical features of this invention, and for easier understanding of the invention. However, it is to be understood that the present invention is not limited to the technical features and their combinations described below.
(1) A method of fixedly connecting together an externally threaded tube and an internally threaded tube by tight engagement of an externally threaded portion of the externally threaded tube and an internally threaded portion of the internally threaded tube, comprising the steps of: performing a wrenching operation in which the externally and internally threaded tubes are rotated relative to each other with the externally and internally threaded portions engaging each other while an axial force is applied to the tubes for forcing the tubes toward each other; detecting a wrenching torque being applied to rotate the tubes relative to each other; obtaining a physical quantity relating to a coefficient of friction between the tubes, on the basis of the detected wrenching torque and the axial force; determining a terminating condition for terminating the wrenching operation, on the basis of the obtained physical quantity; and terminating the wrenching operation when the terminating condition has been satisfied.
In the tube connecting method according to the form (1) of the invention described above, the physical quantity relating to the coefficient of friction between the two tubes is obtained on the basis of the detected wrenching torque and the axial force, and the terminating condition for terminating the wrenching operation is determined on the basis of the obtained physical quantity. When the determined terminating condition has been satisfied, the wrenching operation is terminated. For instance, a desired final value of the wrenching torque is determined on the basis of the obtained physical quantity. In this case, it is considered that the terminating condition has been satisfied when the detected actual value of the wrenching torque has reached the determined desired final value. It is obvious that the wrenching torque required for establishing a desired axial or radial tightening force between the externally and internally threaded portions of the tubes increases with an increase in the obtained physical quantity.
Assuming that the mutually contacting portions of the two tubes have nominal configurations and dimensions, the physical quantity increases with an increase in the wrenching torque if the axial force applied to the two tubes is constant. If the wrenching torque is constant, the physical quantity increases with an increase in the axial force. These facts will become apparent from the equations (3), (8) and (28) given in the PREFERRED EMBODIMENTS OF THE INVENTION. It will be understood that the physical quantity relating to the friction coefficient can be obtained on the basis of the wrenching torque and the axial force applied to the tubes. An experiment shows that the accuracy of obtaining the physical quantity is improved with an increase in the axial force applied to the two tubes.
In the present tube connecting method, the physical quantity relating to the friction coefficient is obtained for each pair of the externally and internally threaded tubes which are to be fixed connected together. The obtained physical quantity reflects the condition of the contacting surfaces of the tubes as machined or finished, and the lubricating condition of the contacting surfaces, for example. Accordingly, a variation in the tightening force applied between the two tubes can be reduced by determining the terminating condition on the basis of the obtained physical quantity relating to the friction coefficient, so that the actual tube tightening force can be controlled to be as close as possible to the nominal or desired value. Therefore, the present method is effective to avoid a yield or seizure of the contacting portions of the tubes, which would otherwise arise from a variation in the tube tightening force. The physical quantity relating to the friction coefficient may be not only the friction coefficient per se, but may also be any quantity from which the friction coefficient can be estimated. For instance, the physical quantity may be a quantity which changes in steps with the friction coefficient.
(2) A method according to the above mode (1), wherein the externally and internally threaded tubes are rotated relative to each other while the tubes are held so as to extend in the vertical direction.
It is desirable to hold the two tubes upright while the two tubes are rotated relative to each other. In this case wherein the two tubes are held upright, the weight of the upper one of the two tubes is applied as the axial force (compressive force) between the two tubes, while the lower tube is held in a stationary or clamped state. Where the upper tube is held in the clamped state, the weight of the lower tube is applied as the axial force (tensile force) between the two tubes. This form of the method does not require an axial force applying device exclusively provided for the purpose of applying the axial force between the two tubes, or permits the use of an axial force applying device having a comparatively small capacity. This form of the method is effective where the method is practiced to obtain a plurality of fixedly connected tubes which constitute a drill pipe used in the vertically extending attitude for supporting a tool for drilling or boring the earth in oil fields, for example. The present form of the method is particularly effective where the next tube is connected to the upper end of the drill pipe when the level of the upper end has become close to the ground level.
(3) A method according to the above form (1), wherein the externally and internally threaded tubes are rotated relative to each while the tubes are held so as to extend in the horizontal direction.
The method according to the above form (3) of the invention is suitable for obtaining a long pipe extending parallel to the ground surface, by fixedly connecting together the externally and internally threaded tubes. Pipes for transporting oils and natural gases are typical examples of such a pipe as obtained according to this form of the invention.
(4) A method according to any one of the above modes (1)-(3), wherein the axial force is applied to the externally and internally threaded tubes for forcing the tubes toward each other.
The wrenching torque applied to the tubes for relative rotation thereof may be detected while an axial compressive force is applied to the two tubes for forcing these tubes toward each other, or alternatively while an axial tensile force is applied to the two tubes for forcing these tubes away from each other. From the standpoint of the construction of a tube connecting apparatus adapted to practice the method, it is preferable to detect the wrenching torque while the axial compressive force is applied between the two tubes. As described later, the coefficient of friction between the contacting shoulder surfaces of the threaded portions of the tubes can be detected with the axial compressive force applied to the tubes, where the two tubes are fixedly connected together with the shoulder surfaces of the threaded portions held in contact with each other.
(5) A method according to the above form (4), wherein the step of detecting a wrenching torque comprises detecting at least one of an initial value of the wrenching torque in an initial phase of the wrenching operation in which shoulder surfaces of the externally and internally tubes are not in contact with each other while thread surfaces of the tubes are in contact with each other, and an intermediate value of the wrenching torque in an intermediate phase of the wrenching operation in which the shoulder surfaces are in substantial contact with each other while the thread surfaces are not in substantial contact with each other.
The method according to the above form (5) is compatible with the methods 1) and 2) described above. In the initial phase, the thread surfaces of the two tubes are in contact with each other. In the intermediate phase, the shoulder surfaces of the tubes are in contact with each other. In the method according to the present form (5), at least one of the physical quantity relating to the coefficient of friction between the contacting thread surfaces and the physical quantity relating to the coefficient of friction between the contacting shoulder surfaces is obtained, and the terminating condition is determined on the basis of the obtained at least one of those two physical quantities. The accuracy of control of the tightening force applied to the tubes can be improved when the terminating condition is determined on the basis of the two physical quantities obtained.
In the initial and intermediate phases, neither an axial tightening force nor a radial tightening force is generated between the contacting thread or shoulder surfaces. In this sense, it is appropriate to obtain the physical quantity or quantities relating to the friction coefficient in the initial and/or intermediate phases. In a final phase following the intermediate phase, an axial tightening force is generated between the contacting thread surfaces and the contacting shoulder surfaces, and the physical quantity relating to the coefficient of friction between the contacting surfaces cannot be obtained with high accuracy.
For simplifying the axial force applying device, it is preferable that the amount and the direction of the axial force applied to the two tubes in the initial direction be the same as those of the axial force applied in the intermediate phase. However, this is not essential. That is, at least one of the amount and the direction in the initial phase may be different from that in the intermediate phase. For instance, an axial tensile force is applied between the two tubes in the initial phase, while an axial compressive force is applied in the intermediate phase. Further, the amount of the axial force applied between the two tubes may be changed during the wrenching operation. The physical quantity relating to the friction coefficient may be obtained on the basis of two or more combinations of the axial force and the wrenching torque value. As described above, the accuracy of obtaining the physical quantity and the accuracy of determination of the terminating condition can be improved by increasing the axial force to thereby increase the initial and intermediate torque values.
(6) A method according to any one of the above modes (1)-(5), wherein the externally and internally threaded portions are tapered threaded portions, and the wrenching torque is detected while a radial tightening force is not generated between the tapered threaded portions.
The method according to the above form (6) is particularly compatible with the method 3) indicated above, but is also compatible with the methods 1 and 2). Where the threaded portions are tapered, a radial tightening force is not generated between the contacting thread surfaces in the initial phase of the wrenching operation, and is generated therebetween in the final phase. In view of this fact, the physical quantity relating to the friction coefficient is obtained in the initial phase, so that the physical quantity can be obtained with high accuracy, without an influence of the radial tightening force.
(7) A method according to any one of the above modes (1)-(6), wherein the wrenching torque is detected in an initial phase of the wrenching operation in which leading franks of the externally threaded portion of the externally threaded tube contact leading franks of the internally threaded portion of the internally threaded tube.
The method according to the above form (7) is compatible with the methods 1), 2) and 3) described above. In the present method, the physical quantity can be detected with high accuracy in the initial phase, since neither an axial tightening force nor a radial tightening force is generated in the initial phase, as described above. In most cases, the franks of the two tubes which contact each other in the initial phase are different from the franks which contact each other in the final phase. Provided that the condition of the thread surfaces as machined and the lubricating condition of the thread surfaces are uniform over the entire areas of the externally and internally threaded portions, the physical quantity obtained in the initial phase can be considered to be the physical quantity relating to the coefficient of friction between the thread franks which contact each other in the final phase.
(8) A method according to any one of the above forms (5)-(7), wherein the step of obtaining a physical quantity comprises obtaining, on the basis of the physical quantity obtained in the initial phase, a physical quantity relating to a coefficient of friction between surfaces of the externally and internally threaded tubes which contact each other in a final phase of the wrenching operation.
As described above with respect to the above form (7), the physical quantity relating to the coefficient of friction between the surfaces of the tubes which contact each other in the initial phase can be considered to be equal to the physical quantity relating to the coefficient of friction between the surfaces of the tubes which contact each other in the final phase, provided that the surface conditions of the tube are uniform over the entire areas of the threaded portions. Where the surface conditions of the surfaces of the tubes which contact each other in the initial phase are different from those of the surfaces which contact each other in the final phase, the physical quantity relating to the coefficient of friction between the surfaces of the tubes contacting each other in the final phase may be estimated by multiplying the physical quantity obtained in the initial phase by a predetermined factor. In this respect, it is noted that a variation in the surface condition of the threaded portion of each tube is generally smaller than a variation in the surface condition of different tubes.
(9) A method according to any one of the above modes (1)-(8), wherein the externally and internally threaded tubes are rotated relative to each other with the wrenching torque being applied to the tubes at radial positions of outer circumferential surfaces of the tubes.
Where the tubes are relatively long, it is relatively difficult to rotate the two tubes relative to each other by applying the wrenching torque to the tubes at axial end portions of the tubes which are remote from the externally and internally threaded portions. In this case, therefore, it is desirable to apply the wrenching torque to the tubes at the radial positions of the outer circumferential surfaces of the tubes, and at the axial positions which are relatively close to the externally and internally threaded portions. It is also desirable to apply the axial force to the tubes at their outer circumferential surfaces.
(10) A method according to any one of the above forms (1)-(9), wherein the externally and internally threaded tubes are rotated relative to each other such that one of the externally and internally threaded tubes is held stationary while the other of the tubes is rotated with the axial force being applied to the above-indicated other tube.
For rotating the externally and internally threaded tubes relative to each other while applying the axial force to the two tubes, a selected one of the following three modes of applying the axial force to the tubes is combined with a selected one of the following three modes of rotating the tubes relative to each other:
Axial Force Applying Modes
Mode 1 in which the axial force is applied to the externally threaded tube while the internally threaded tube is held stationary in the axial direction;
Mode 2 in which the axial force is applied to the internally threaded tube while the externally threaded tube is held stationary in the axial direction; and
Mode 3 in which the axial force is applied to both of the externally and internally threaded tubes.
Rotating Modes
Mode A in which the externally threaded tube is rotated relative to the internally threaded tube which is held stationary in the circumferential direction;
Mode B in which the internally threaded tube is rotated relative to the externally threaded tube which is held stationary in the circumferential direction; and
Mode C in which both of the externally and internally threaded tubes are rotated.
Where a tube assembly to be obtained from time to time by fixedly connecting two or more pairs of the externally and internally threaded tubes is relatively long, it is desirable that the tube which is connected to one end of the already obtained tube assembly be rotated relative to the already obtained tube assembly while the axial force is applied to the tube being rotated.
(11) A method according to any one of the above forms (1)-(10), wherein the terminating condition is satisfied when an actual value of the wrenching torque has become equal to a desired final value of the wrenching torque which is determined on the basis of the physical quantity.
(12) A method of checking a wrenching operation in which an externally threaded tube and an internally threaded tube are rotated relative to each other, to fixedly connect together the externally and internally threaded tubes by tight engagement of an externally threaded portion of the externally threaded tube and an internally threaded portion of the internally threaded tube, the method comprising (a) determining an upper limit and a lower limit which define an optimum range of a relative rotation speed of the tubes, and an upper limit and a lower limit which define an optimum range of a wrenching torque applied to the tubes for relative rotation of the tubes, (b) determining that the wrenching operation is performed in a normal manner if one of a first condition and a second condition is satisfied, the first condition being satisfied when the relative rotation speed is within the optimum range thereof when the wrenching torque has reached the lower limit thereof, the second condition being satisfied when the wrenching torque is within the optimum range thereof when the relative rotation speed has reached the lower limit thereof, and (c) determining that the wrenching operation is performed in an abnormal manner if neither the first condition nor the second condition is satisfied, the method further comprising the steps of:
applying an axial force to the externally and internally threaded tubes for at least a portion of a period in which the tubes are in substantially contact with each other only at thread surfaces of the externally and internally threaded portions;
obtaining a physical quantity relating to a coefficient of friction between the tubes, on the basis of the axial force and the wrenching torque which are applied to the tubes; and
determining the lower and upper limits of the wrenching torque on the basis of the obtained physical quantity.
(13) An apparatus for performing a wrenching operation to fixedly connect together an externally threaded tube having an externally threaded portion and an internally threaded tube having an internally threaded portion, the apparatus comprising:
a rotary drive device for rotating the externally and internally threaded tubes relative to each other with the externally and internally threaded portions engaging each other;
an axial force applying device for applying an axial force to the tubes for at least a portion of a period in which the tubes are rotated by the rotary drive device relative to each other, without generation of a tightening force between the tubes;
a torque detecting device for detecting a wrenching torque applied by the rotary drive device to the tubes for relative rotation thereof while the axial force is applied to the tubes by the axial force applying device;
a physical quantity obtaining device for obtaining a physical quantity relating to a coefficient of friction between the tubes, on the basis of the wrenching torque detected by the torque detecting device and the axial force applied by the axial force applying device; and
a terminating condition determining device for determining a terminating condition for terminating the wrenching operation, on the basis of the physical quantity obtained by the physical quantity obtaining device.
The tube connecting apparatus constructed according to the above form (13) of the present invention is capable of practicing the method according to the above form (1) of the invention. The axial force applying device may be arranged to keep applying the axial force throughout the wrenching operation, or apply the axial force for a predetermined portion of the wrenching operation, or two or more times in an intermittent fashion. The axial force applying device may be a support device arranged to support one of the two tubes such that the weight of that one tube acts between the tubes as the axial force. The torque detecting device may be operated only once during the wrenching operation, to detect a single value of the wrenching torque, or two or more times during the wrenching operation, to detect a plurality of wrenching torque values. In the latter case, the physical quantity relating to the friction coefficient can be obtained with higher accuracy, on the basis of the detected wrenching torque values. A termination commanding device may be provided to automatically terminate the wrenching operation by turning off the rotary drive device, when the terminating condition determined by the terminating condition determining device has been satisfied. This arrangement permits automatic termination of the wrenching operation when the actual wrenching torque value has reached the desired final wrenching value. Although this arrangement is ideal, it is not essential. For instance, an indicator such as a buzzer may be provided so that the indicator is operated when the terminating condition has been satisfied, to inform the operator of the apparatus that the terminating condition has been satisfied. In this case, the operator turns off the rotary drive device or terminate the wrenching operation in response to the operation of the indicator.
(14) An apparatus according to the above form (13), wherein the rotary drive device comprises:
a rotary drive source;
a clamping device for clamping one of the externally and internally threaded tubes to a frame structure of the apparatus such that the one of the tubes is not rotatable relative to the frame structure; and
a rotary motion transmitting device including a chucking device which holds or chucks the other of the tubes such that the above-indicated other tube is not rotatable relative to the chucking device, the rotary motion transmitting device transmitting a rotary motion of the drive source to the above-indicated other tube through the chucking device.
In the rotary drive device of the tube connecting apparatus according to the above form (14) of the invention, one of the two tubes is clamped while the above-indicated other tube is rotated by the rotary motion of the rotary drive device transmitted thereto by the motion transmitting device through the chucking device. The motion transmitting device may include a first gear fixed to the output shaft of the rotary drive source, and a second gear which is fixed to the chucking device and which meshes with the first gear. Alternatively, the motion transmitting device includes a pulley fixed to the output shaft of the rotary drive source, a pulley fixed to the chucking device, and a timing belt connecting these two pulleys. Where a long pipe is obtained by fixedly connecting together the externally and internally threaded tubes, as described above, the tube which is connected to an already obtained tube assembly is desirably rotated, since the rotation of this tube only relative to the already obtained tube assembly can be achieved with a comparatively small wrenching torque (rotary drive force), and the rotary drive device can be made comparatively small-sized and is accordingly available at a reduced cost.
(15) An apparatus according to the above form (14), wherein the chucking device includes a plurality of part-cylindrical members which are butted together at opposite ends of each of the part-cylindrical members in planes parallel to an axis of the above-indicated other tube, the part-cylindrical members cooperating to form a cylindrical clamping structure of split type which has an axis aligned with the axis of the above-indicated other tube and which is disposed radially outwardly of the above-indicated other tube, for contact with an outer circumferential surface of the above-indicated other tube to hold the other tube.
The part-cylindrical members of the split type cylindrical clamping structure may first be disposed radially outwardly of the outer circumferential surface of an axially intermediate portion of the above-indicated other tube, and then butted together and connected to each other by a suitable connecting or locking device, so that the split type cylindrical clamping structure is fastened to the tube such that the tube is not rotatable relative to the clamping structure. If the chucking device uses a one-piece annular or cylindrical clamping member, this clamping member must be removed in the axial direction from the threaded end portion toward the other end portion after the above-indicated other tube is fixedly connected to the above-indicated one tube. To the contrary, the split type cylindrical clamping structure can be easily removed from the tube, for instance, in the radial direction. The split-type cylindrical clamping structure may consist of at least two part-cylindrical members, for instance, three part-cylindrical members. The part-cylindrical members butted together at their ends may be connected together with connector screws extending substantially in the circumferential direction of the cylindrical clamping structure, so that the part-cylindrical members are held in pressing contact with the outer circumferential surface of the tube. However, the removal of the clamping structure can be made easier by using such connector screw or screws at only one circumferential position of the structure, and using pivotal connectors at the other circumferential positions, so that the adjacent part-cylindrical members are connected to each other pivotally about a connector pin extending in the axial direction of the clamping structure. In this case, the connector screw or screws provided at the single circumferential position is/are tightened the split type cylindrical clamping structure is fastened to the tube with the part-cylindrical members in pressing contact with the outer circumferential surface of the tube.
(16) An apparatus according to the above form (15), wherein the cylindrical clamping structure has a locking portion projecting in an axial direction thereof from axial end faces of at least two of the plurality of the part-cylindrical members, the cylindrical clamping structure being locked at the locking portion for holding the above-indicated other tube.
Where the locking portion projects in the axial direction from the part-cylindrical members but does not project in the radially outward direction from the outer part-cylindrical surface of the part-cylindrical members, the wrenching torque can be applied to the above-indicated other tube at its outer circumferential surface. The locking portion projecting from the axial end faces may include a portion which projects in the radially outward direction of the cylindrical clamping structure.
(17) An apparatus according to the above mode (14), wherein the chucking device includes an annular member having an inside diameter larger than an outside diameter of the above-indicated other tube, and an interposed member which is interposed between an inner circumferential surface of the annular member and an outer circumferential surface of the above-indicated other tube, such that the wrenching torque is transmittable from the annular member to the above-indicated other tube.
The interposed member may be three or more radial screws which are screwed in respective tapped holes through the annular member so as to extend in the radial direction and which have heads for contact with the outer circumferential surface of the above-indicated other tube. For fastening the annular member to the tube, the radial screws are first screwed in the radially outward direction of the annular member, and the annular member is positioned radially outwardly of the tube. Then, the radial screws are screwed in the radially inward direction so that the heads of the screws contact the outer circumferential surface of the tube, to permit the wrenching torque to be transmitted to the tube. The radial screws may be replaced by radial pins, which are movable in the radially outward and inward directions by a suitable actuator. The interposed member may be constructed according to the following form (18).
(18) An apparatus according to the above mode (17), wherein one of the annular member and the interposed member has a first tapered inner circumferential surface whose diameter increases in one of opposite axial directions of the annular member, and the interposed member has a second tapered outer circumferential surface whose diameter decreases in the one of the opposite axial directions, the interposed member further having an inner circumferential surface whose diameter is constant in the opposite axial directions, the interposed member consisting of a plurality of part-cylindrical wedge members which are butted together in planes parallel to the axis of the above-indicated other tube when the part-cylindrical wedge members are pressed in the one of the opposite axial directions into an annular gap between the first tapered inner circumferential surface and the outer circumferential surface of the above-indicated other tube, for holding the above-indicated other tube such that the wrenching torque is transmittable from the annular member to the other tube, the chucking device further including a pressing device for pressing the plurality of part-cylindrical wedge members of the interposed member into the annular gap.
The pressing device is arranged to press the plurality of part-cylindrical wedge members of the interposed member in between the annular member and the above-indicated other tube. The simplest form of the pressing device includes a pressure portion which extends radially outwardly from each of the wedge members and which has through-holes formed therethrough in the axial direction. In this case, the pressing device further includes pressure screws which are screwed through the respective through-holes into respective tapped holes formed in one axial end face of the annular member. By tightening the pressure screws, the pressure portion is axially moved with the part-cylindrical wedge members toward the annular member, whereby the wedge members are interposed between the annular member and the tube. Preferably, the annular member has the first tapered inner circumferential surface, and the interposed member is a tapered cylindrical wedge consisting of a plurality of part-cylindrical wedge pieces which cooperate to define the second tapered outer circumferential surface for sliding contact with the first tapered inner circumferential surface, and the straight inner circumferential surface for sliding contact with the outer circumferential surface of the tube. This arrangement permits a larger maximum amount of the wrenching torque to be transmitted to the tube through the annular member and the tapered cylindrical wedge. The part-cylindrical wedge pieces may be obtained by cutting a tapered cylindrical wedge member in respective planes parallel to and including its axis. The chucking device according to the above form (18) wherein the annular member have the continuous outer circumferential surface without butting seams, the wrenching torque can be more easily transmitted to the annular member, than in the chucking device which includes a plurality of part-cylindrical members which are butted together for contact with the outer circumferential surface of the tube.
(19) An apparatus according to any one of the above forms (14)-(18), wherein the rotary drive device includes one of an electric motor and a fluid-actuator motor.
The fluid-actuator motor includes a hydraulically operated motor and a pneumatically operated motor. The fluid-actuator motor is capable of producing a relatively large torque with a relatively small size, and is therefore suitable for the rotary drive device which is required to rotate the tubes relative to each other at a comparatively low speed with a comparatively high torque. The electric motor is preferably equipped with a speed reducer.
(20) An apparatus according to any one of the above forms (13)-(19), wherein the rotary drive device is a hydraulically operated rotary drive device including a hydraulic cylinder, a chucking device for clamping the above-indicated other tube, and a motion converting device for converting a linear motion of the hydraulic cylinder into a rotary motion of the chucking device, the above-indicated other tube being rotated by rotation of the chucking device by operation of the hydraulic cylinder.
(21) An apparatus according to any one of the above forms (13)-(19), wherein both of the externally and internally threaded tubes are positioned so as to extend in a vertical direction, and the axial force applying device includes vertically holding device for holding one of the tubes such that a weight of the above-indicated one tube acts as the axial force between the externally and internally threaded portions of the tubes.
(22) An apparatus according to any one of the above forms (13)-(21), wherein the axial force applying device includes a forcing device for applying the axial force to the externally and internally threaded tubes such that the tubes are forced toward each other by the axial force.
(23) An apparatus according to any one of the above forms (13)-(22), wherein the rotary drive device includes a clamping device for clamping one of the externally and internally threaded tubes to a frame structure of the apparatus such that the above-indicated one tube is not rotatable relative to the frame structure, the rotary drive device rotating the other of the tubes relative to the above-indicated one tube,
and wherein the axial force applying device applies the axial force to the above-indicated other tube while the above-indicated one tube is held by the frame structure such that the above-indicated one tube is not axially movable relative to the frame structure.
The apparatus can be small-sized, by constructing the rotary drive device and the axial force applying device so that one of the two tubes is held by the frame structure such that this one tube is neither rotatable nor axially movable relative to the frame structure, and so that the axial force is applied to the other tube by the axial force applying device while this other tube is rotated by the rotary drive device relative to the above-indicated one tube. Where a long pipe is obtained by fixedly connecting together the externally and internally threaded tubes, as described above, it is desirable to apply the wrenching torque and the axial force to the tube which is connected to an already obtained tube assembly.
(24) An apparatus according to the above form (23), wherein the axial force applying device includes:
at least one axially forcing roller disposed such that an outer circumferential surface of the at least one axially forcing roller is held in contact with an outer circumferential surface of the above-indicated other tube;
a roller support structure which supports the at least one axially forcing roller such that the at least one axially forcing roller is rotatable about an axis thereof;
a holder device which holds the roller support structure in the frame structure such that the roller support structure is immovable in axial and radial directions of the above-indicated other tube and is rotatable about an axis of the other tube; and
a roller drive device disposed on the roller support structure and operable to rotate the at least one axially forcing roller.
In the apparatus according to the above form (24) wherein the roller support structure is held in the frame structure such that the roller support structure is not movable in the axial and radial directions of the above-indicated other tube while it is rotatable about the axis of the tube. This arrangement permits the application of the axial force to the above-indicated other tube while this tube is rotated. Where the roller drive device is operable bidirectionally, it is possible to selectively apply either an axial compressive force or an axial tensile force between the two tubes.
(25) An apparatus according to the above form (24), wherein the holder device includes an annular rail fixed to the frame structure coaxially with the other tube, and at least three support rollers attached to the roller support structure such that the at least three support rollers are arranged in a circumferential direction of the other tube, the at least three support rollers being held in rolling engagement with the annular rail.
The three or more support rollers are required to be arranged along the outer circumferential surface of the above-indicated other tube over an angular range of at least 180xc2x0 about the axis of the tube. Preferably, the support rollers are equiangularly spaced apart from each other over the full angular range of 360xc2x0. With these three or more support rollers held in rolling contact with the inner circumferential surface of the annular rail, the roller support structure is positioned coaxially with the annular rail and is rotatable relative to the annular rail. The support rollers and the annular rail may be arranged such that the support rollers engage the annular rail, so as to prevent a movement of the roller support structure relative to the annular rail in the axial direction of the annular rail. However, it is preferable to provide two sets of support rollers and corresponding to annular rails. The first set of at least three support rollers is attached to the roller support structure such that the support rollers are positioned radially outwardly of the roller support structure, while the second set of at least three support rollers is attached to one of the opposite axial end faces of the roller support structure. The first annular rail is disposed coaxially with and radially outwardly of the roller support structure, for engagement with the support rollers of the first set, while the second annular rail is disposed on one of the axially opposite sides of the roller support structure and is radially aligned with the roller support structure. In this preferred arrangement, the axial force applied to the roller support structure is received by the second set of support rollers and the corresponding second annular rail. Where the second set of support rollers and the second annular rails are arranged to engage with each other so as to prevent a radial movement of the roller support structure relative to the second annular rail, the first set of support rollers and the first annular rail may be eliminated.
The axial force applying device preferably includes a plurality of axially forcing rollers, which are desirably arranged in the circumferential direction of the above-indicated other tube in an equiangularly spaced-apart relation with each other. The roller support structure which support the two or more axially forcing rollers may be a one-piece annular member disposed in a radially opposed relation with the annular rail over the full 360xc2x0 angular range. It is desirable, however, that the roller support structure consists of a plurality of roller support members each of which has a central angle of not larger than 180xc2x0. Where the annular rail also consists of a plurality of part-cylindrical rail members which are separable from each other when the corresponding portions of the frame structure are separated from each other, as described later, the roller support members as well as the rail members can be radially positioned relative to the above-indicated tube, when the corresponding portions of the frame structure is positioned. Each of the roller support members supports at least one axially forcing roller.
(26) An apparatus according to any one of the above forms (13)-(23), wherein the axial force applying device includes:
an axial force applying member fixed to one of the externally and internally threaded tubes such that the axial force applying member is coaxial with the one tube and is not movable relative to the one tube in an axial direction of the one tube; and
an axial drive device disposed between the axial force applying device and the frame structure and operable to apply the axial force to the axial force applying member in at least one of opposite axial directions of the tubes, while permitting rotation of the axial force applying member relative to the frame structure.
For example, the axial drive device includes: a movable member supported by the frame structure such that the movable member is movable in the axial direction of the tubes; at least one axial force applying roller fixed to the movable member such that each axial force applying roller is rotatable relative to the movable member, for rolling contact with the axial force applying member, at a position on a circle concentric with the above-indicated one tube, when the axial force applying member is rotated with the above-indicated one tube; and an actuator connected to the frame structure and the movable member and operable to move the movable member to force each axial force applying against the axial force applying member in the axial direction of the one tube. The actuator may be a fluid-actuated cylinder. This arrangement permits the application of the axial force to the axial force applying member while the at least one axial force applying roller permits the axial force applying member to be rotated with the above-indicated one tube. The axial force applying member may be either independent of an annular chucking member for holding or chucking a drive member to the above-indicated one tube for rotating this tube, or a portion of that chucking member.
(27) An apparatus according to any one of the above forms (13)-(26), wherein the axial force applying device includes an impact force applying device for applying an impact force to the externally and internally threaded tubes as the axial force.
For instance, the impact force applying device includes: an axial force applying member fixed to one of the two tubes; an inertia mass disposed such that the inertia mass is movable relative the axial force applying member in an axial direction of the tubes; and an impact drive device operable to apply the impact force between the axial force applying member and the inertia mass, so as to move the inertia mass toward or away from the axial force applying member. In this arrangement, an operation of the impact drive device causes the impact force to be applied to the axial force applying member based on an inertial force of the inertia mass, so that the impact force is applied to the above-indicated one tube through the axial force applying member. Since the generation of the axial impact force does not require the inertia mass and the impact drive device to be supported by the frame structure of the apparatus, the inertia mass and the impact drive device may be supported by the axial force applying member. In this case, the inertia mass and the impact drive device are rotated with the axial force applying device.
(28) An apparatus according to any one of the above forms (23)-(27), wherein the rotary drive device includes a hydraulic cylinder, a chucking device for holding the other tube, and a motion converting device for converting a linear motion of the hydraulic cylinder into a rotary motion of the chucking device, the hydraulic cylinder being operated to rotate the chucking device for thereby rotating the other tube,
and wherein the terminating condition determining device determines a desired final value of the wrenching torque on the basis of the physical quantity obtained by the physical quantity obtaining device, the apparatus further comprising a termination determining device for determining that the terminating condition is satisfied when the wrenching torque obtained on the basis of the hydraulic pressure has become equal to the desired final value.
In the tube connecting apparatus constructed according to the above form (28) of this invention wherein the above-indicated other tube is rotated by an operation of the hydraulic cylinder, the relatively large wrenching torque can be easily applied to the tube. The tube is rotated by the rotary motion of the chucking device which is obtained by conversion of the linear motion of the hydraulic cylinder by the motion converting device. This arrangement makes it difficult to obtain a large angle of rotation of the tube from a single linear motion of the hydraulic cylinder. To rotate the tube by a desired angle, it is usually required to repeatedly operate the hydraulic cylinder in the opposite directions while alternately placing the chucking device in the clamping and non-clamping positions. While the present rotary drive device can be used in the initial and intermediate phases of the wrenching operation, it is particularly suitable for rotating the tube in the final phase only.
For improved stability of application of a large wrenching torque to the tube and for fast clamping and unclamping of the tube by the chucking device, the chucking device is desirably a hydraulically operated device for holding the tube to be rotated. For instance, the hydraulically operated chucking device may include clamping members which are movable between an open position and a closed position in a diametric direction of the tube. In this case, the tube is clamped in the closed position of the clamping members, such that the tube is aligned with the center of the chucking device by a radial movement of the tube by the clamping members. However, this arrangement is not essential. The chucking device may include an annular chucking member in which the tube to be rotated is chucked at a suitable axial portion. In this case, the tube is moved in the axial direction so as to extend through the annular chucking member.
In the apparatus according to the above form (28), the hydraulic cylinder may be considered to serve as the rotary drive source, and the chucking device and the motion converting device may be considered to serve as a rotary drive force transmitting device.
(29) An apparatus according to any one of the above forms (23)-(28), wherein the rotary drive device includes a rotary motor for rotating the other tube, and the torque detecting device detects the wrenching torque on the basis of an operating state of the rotary motor.
The rotary drive device may include both the hydraulic cylinder provided in the apparatus according to the above form (28) and the rotary motor provided in the apparatus according to the above form (29), the tube can be rotated by the rotary motor in the initial and intermediate phases of the wrenching operation, and by the hydraulic cylinder in the final phase of the wrenching operation. The rotary motor may be either a hydraulic motor or an electric motor. In either case, the wrenching torque is detected on the operating state of the rotary motor in at least one of the initial and intermediate phases, and the desired final value of the wrenching torque is obtained on the basis of the detected wrenching torque.
Where the rotary drive device includes only the rotary motor and does not include the hydraulic cylinder, the rotary motor is preferably a hydraulic motor. In this case, the hydraulic motor is operated in the initial and intermediate phases at a relatively high speed to produce a relatively small torque, with a pressurized fluid delivered from a hydraulic pump whose delivery pressure is relatively low and whose delivery rate is relatively high, and in the final phase at a relatively low speed to produce a relatively large torque, with a pressurized fluid delivered from a hydraulic pump whose delivery pressure is relatively high and whose delivery rate is relatively low. This arrangement permits the single hydraulic motor to rotate the tube throughout the wrenching operation from the initial phase to the final phase. In this case, the wrenching torque can be detected on the basis of the hydraulic pressure at the hydraulic motor, and the desired final wrenching torque value can be obtained on the basis of the detected wrenching torque. Further, the apparatus may comprise a termination determining device which determines that the terminating condition is satisfied when the wrenching torque detected on the basis of the hydraulic pressure of the hydraulic motor has reached the desired value.
(30) An apparatus according to the above form (29), wherein the rotary motor is a hydraulic motor, and the torque detecting device includes a pressure detector for detecting a hydraulic pressure in the hydraulic motor.
(31) An apparatus according to any one of the above forms (13)-(30), wherein the physical quantity obtaining device includes an axial force detecting device which detects the axial force applied to the tubes by the axial force applying device, the physical quantity obtaining device estimating the coefficient of friction on the basis of the axial force detected by the axial force detecting device and the wrenching torque detected by the torque detecting device.
If the axial force applied by the axial force applying device is held constant at a known value, the axial force detecting device may be eliminated. However, the provision of the axial force detecting device permits the estimation of the friction coefficient on the basis of the axial force and the wrenching torque which are detected at the same point of time, so that the axial force need not be held constant, assuring an increased freedom in the control of the wrenching operation. It is noted that the use of the axial force detected by the axial force detecting device improves the accuracy of estimation of the friction coefficient, even where the applied axial force is held constant at a given value.
(32) An apparatus according to the above forms (13)-(31), wherein the torque detecting device includes a torsional torque detecting device for detecting a torsional torque applied to a rotary shaft in the rotary drive device.
(33) An apparatus according to any one of the above forms (13)-(32), wherein the rotary drive device includes:
a rotary drive source;
a clamping device for clamping one of the externally and internally threaded tubes to a frame structure such that the one tube is not rotatable relative to the frame structure;
a rotary motion transmitting device for transmitting a rotary motion of the rotary drive source to the other of the tubes; and
a drive source holder device for holding the rotary drive source such that the rotary drive source is axially movable relative to the frame structure and is not rotatable about an axis thereof,
and wherein the torque detecting device includes a reaction force detecting device which detects a reaction force which is applied to the drive source holder device as a result of rotation of the other tube.
The wrenching torque is represented by a product of the detected reaction force and a distance between the axis of the tubes and the reaction force detecting device.
(34) An apparatus according to any one of the above forms (13)-(31), wherein the rotary drive device includes an electric motor as a rotary drive source, and the torque detecting device detects the wrenching torque on the basis of an electric current flowing through the electric motor.
(35) An apparatus according to any one of the above forms (13)-(34), further comprising a frame structure consisting of a plurality of separate elements positioned radially outwardly of the tubes such that the elements are arranged in a circumferential direction of the tubes, and a fixing device for fixing the separate elements to each other such that the separate elements are butted together in planes parallel to an axis of the tubes, so as to surround portions of outer circumferential surfaces of the tubes.
The frame structure of the apparatus which surround the circumference of the tubes may be a one-piece structure. In this case, however, the tubes must be set into and removed from the apparatus by moving the tubes in the axial direction. These setting and removing operations involving the axial movements of the tubes are cumbersome and time-consuming. On the other hand, the frame structure consisting of the separate elements butted together in the above-indicated planes facilitates these operations, since the separate elements permits the tubes to be moved in the radial direction while the separate elements are not fixed to each other.
(36) An apparatus according to any one of the above forms (13)-(35), further comprising an intermediate phase detecting device for detecting at least one point of time in an intermediate phase of the wrenching operation.
(37) An apparatus according to the above form (36), wherein the intermediate phase detecting device detects the at least one point of time on the basis of the wrenching torque detected by the torque detecting device.
(38) An apparatus according to the above form (36) or (37), wherein the intermediate phase detecting device includes a device for detecting a moment of initiation of the intermediate phase depending upon a rapid change of a rate of change of the detected wrenching torque, which rapid change takes place upon transition of the wrenching operation from an initial phase to the intermediate phase.
Upon transition of the wrenching operation from the initial phase to the intermediate phase, there arises a rapid increase or a rapid decrease of the detected wrenching torque, depending upon the configurations and dimensions of the two tubes. In either case, the wrenching torque rapidly changes due to a change in the contacting surfaces of the two tubes.
(39) An apparatus according to any one of the above forms (36)-(38), wherein the intermediate phase detecting device includes:
torque memory means for storing values of the wrenching torque which are detected from time to time by the torque detecting device; and
determining means for determining a moment of termination of the intermediate phase on the basis of the values of the wrenching torque stored in the torque memory means, after the detected wrenching torque has reached a predetermined value.
The moment of transition from the intermediate phase to the final phase, namely, the moment of termination of the intermediate phase can be detected on the basis of the detected values of the wrenching torque which are stored from time to time in the torque memory means. However, the desired final wrenching torque value corresponding to the desired tightening force of the tubes must have been determined before the actual tightening force has increased to the desired value. To this end, it is desirable to determine the moment of termination of the intermediate phase as early as possible. Accordingly, it is desirable that the predetermined value of the wrenching torque indicated above be as small as possible to the extend that permits the moment of the termination to be determined.
(40) An apparatus according to any one of the above forms (13)-(39), further comprising a final phase detecting device which detects a final phase of the wrenching operation in which at least one of an axial tightening force and a radial tightening force is generated between the externally and internally threaded portions of the tubes.
As described above, the final phase directly follows the initial phase, or alternatively the final phase follows the intermediate phase which follows the initial phase. In either case, the transition to the final phase can be detected on the basis of a change in the rate of change of the detected wrenching torque, or on the basis of the detected wrenching torque values. For instance, the transition torque value corresponding to the moment of transition to the final phase is obtained on the basis of the physical quantity relating to the friction coefficient, which quantity is obtained in the initial or intermediate phase. The moment of the transition is detected when the actual wrenching torque has reached the transition torque value.
(41) An apparatus according to any one of the above forms (13)-(40), wherein the terminating condition determining device determines a desired final value of the wrenching torque on the basis of the physical quantity obtained by the physical quantity obtaining device, the apparatus further comprising:
a termination determining device for determining that the terminating condition is satisfied when the actual value of the wrenching torque has become equal to the desired final value.
(42) An apparatus according to any one of the above forms (13)-(41), further comprising a thread engagement abnormality detecting device which detects an abnormality associated with mutual meshing engagement of the externally and internally threaded portions of the tubes, on the basis of an initial value of the wrenching torque detected by the torque detecting device in an initial phase of the wrenching operation.
The wrenching torque value in the initial phase of the wrenching operation becomes abnormally large if there arises an abnormality associated with mutual engagement of the externally and internally threaded portions of the tubes, such as the presence of foreign matters between the contacting thread surfaces, or abnormal meshing engagement of the thread surfaces. For example, the thread engagement abnormality detecting device includes tolerable range setting means for setting a tolerable range of the initial wrenching torque value, on the basis of appropriate data such as the nominal pitch diameter and lead of the threads, and abnormality judging means for determining that there exists an abnormality associated with the mutual meshing engagement of the externally and internally threaded portions of the tubes, if the detected initial wrenching torque value is outside the tolerable range. This arrangement permits early detection of the abnormality. The apparatus may further comprise emergency stop means for turning off the rotary drive device when the abnormality judging means detects the presence of an abnormality associated with the thread engagement. This emergency stop means is effective to prevent undesirable continuation of the wrenching operation in the presence of the thread engagement abnormality.
(43) An apparatus according to any one of the above forms (13)-(42), wherein the physical quantity obtaining device and the terminating condition determining device comprise a computer connected to at least the torque detecting device.
(44) A computer-readable recording medium storing a wrenching torque control program to be executed for performing a wrenching operation to fixedly connect together an externally threaded tube having an externally threaded portion and an internally threaded tube having an internally threaded portion, the wrenching control program comprising the steps of:
obtaining a physical quantity relating to a coefficient of friction between the externally and internally threaded tubes, on the basis of a wrenching torque and an axial force being applied to the tubes while the tubes are rotated relative to each other by the wrenching torque, with the externally and internally threaded portions engaging each other while the axial force is applied so as to act between the tubes; and
determining a terminating condition for terminating the wrenching operation, on the basis of the obtained physical quantity.
The tube connecting apparatus constructed according to the above form (13) of this invention may be equipped with a computer adapted to read and execute the wrenching control program stored in the recording medium according to the above form (44). This tube connecting apparatus is capable of practicing the tube connecting method according to the above form (1) of the invention. The wrenching control program may be formulated to practice any one of the technical features according to the above forms (2)-(11).
(45) A method of fixedly connecting together an externally threaded member and an internally threaded member by tight engagement of an externally threaded portion of the externally threaded member and an internally threaded portion of the internally threaded member, comprising the steps of:
performing a wrenching operation in which the externally and internally threaded members are rotated relative to each other with the externally and internally threaded portions engaging each other while an axial force is applied so as to act between the members;
detecting a wrenching torque being applied to rotate the members relative to each other;
obtaining a physical quantity relating to a coefficient of friction between the members, on the basis of the detected wrenching torque and the axial force;
determining a terminating condition for terminating the wrenching operation, on the basis of the obtained physical quantity; and
terminating the wrenching operation when the terminating condition has been satisfied.
The externally and internally threaded members may be substantially solid shaft members. Although the primary object of the present invention is to provide an improvement in the field of connecting threaded tubes, the principle of the invention is also applicable to the connection of threaded members other than threaded tubes or pipes. The method according to the above form (45) includes any one of the technical features according to the above forms (2)-(11). The tube connecting apparatus according to the above form (13) may be used as an apparatus for fixedly connecting externally and internally threaded members. This apparatus may include any one of the technical features according to the above forms (14)-(34).